The present invention relates to storage subsystems (storage controller) with a function of virtualizing a common storage volume from them, and to a load balancing method thereof.
In a database system handling large amount of data in a data center or the like, data is stored in a storage subsystem such as a disk array system. A disk array system has a plurality of storage devices disposed in an array, and provides its storage volumes configured in RAID (Redundant Arrays of Independent Inexpensive Disks) to a host system. The host system and the storage subsystem are mutually connected via a device sharing network such as a SAN (Storage Area Network). Regarding a functionality of such a storage subsystem, Japanese Patent Laid-Open Publication No. 2005-165444 proposes a method of virtualizing a storage volume in an external storage subsystem as its storage volume and making it assignable to a host computer. Further, Japanese Patent Laid-Open Publication No. 2003-316522 proposes a method of absorbing the difference in functions or specification of a plurality of storage subsystems, and comprehensively utilizing the functions of the plurality of storage subsystems.